Description: (Applicant's Description) The Xiphophorus Genetic Stock Center at Southwest Texas State University will serve as the core facility for the Program Project because (1) all stocks necessary for the production of hybrid and backcross hybrid fishes required in the Program Project are maintained as pedigreed lines at the Stock Center, (2) the Stock Center is the only facility within the two research institutions that has the capacity to house and feed the estimated 2,000 animals that will be bred per year during the course of the estimated 2,000 animals that will be bred per year during the course of the project, and (3) proposed experimental treatments with UV and MNU occur early in the life of the backcross hybrids, and since experimental animals must be maintained for six months or more prior to sacrifice, the Stock Center is the most logical facility for headquartering the core. The specific aims of the Core Project are to ensure that (1) parental stocks required to produce hybrids are maintained in sufficient numbers, (2) all hybridizations produce sufficient F1 progeny for backcross matings, (3) backcross offspring are produced in sufficient numbers for the experimental and control of requirements produced in sufficient numbers for the experimental and control requirements of each project (4) backcross offspring receive the precise experimental treatment, i.e., UV irradiation or MNU dosage specified by each project investigator, (5) the health of the entire animal colony is never compromised, and (6) the genetic backgrounds and stock purity of pedigrees used in these experiments are well characterized. Baseline data regarding the genetic backgrounds of parental and F1 hybrid stocks used to manufacture backcross hybrids are necessary, particularly in light of recent findings of polyallelism in isogenic clonal zebrafish stock which suggest that assumptions of stock homogeneity must also be validated in Xiphophorus stocks. Biochemical genetic profiles for each of the stocks will identify candidates for additional hybridization mating required by each component project to continue their linkage map saturation and/or associated tumor marker mapping efforts. Core facility personnel will screen parents of all broods utilized in the Program for more than 50 protein-coding loci after each mating has been terminated and will screen siblings of the animals used in the Program Project. The significance of establishing a core facility for the Program Project is that it will centralize stock management, parental, hybrid, and backcross animal product, experimental treatment, animal core, and stock purity, thereby streamlining the logistics of the Program Project and substantially decreasing the cost of research.